1. exit BOINC
2. go to ProgramData\Boinc directory
3. find cc_config file and edit it with notepad
4. find at the end line use_all_gpus>0</use_all_gpus> and change it to use_all_gpus>1</use_all_gpus> If the option is not there, add it.
5. save it

There is a Wacky GPU memory reporting Bug with the recent Boinc 7 clients, because the available GPU memory is reported wrong, Boinc then doesn't use both GPUs because they aren't similar enough,
Boinc 7.0.36 has a partial fix, But there are changes to the (internal) flops reported for the GPU, and because of the changes, existing GPU Wu's will be on the verge of going Maximum time exceeded,
so any GPU Wu's should be completed prior to upgrading to Boinc 7.0.36 (new GPU Wu's will get a revised <rsc_fpops_est> figure so will complete O.K)

Will be the currently BOINC DEV-V7.0.36 maybe the new recommended version in near future?

Probably not, as it still has half the Wacky GPU memory reporting Bug, in my case it was the total GPU memory that was reported wrong, while the other testers reported it was the available GPU memory that was wrong (that was fixed in 7.0.36),
the fix for the Total GPU memory Bug should be in Boinc 7.0.37

Will be the currently BOINC DEV-V7.0.36 maybe the new recommended version in near future?

Probably not, as it still has half the Wacky GPU memory reporting Bug, in my case it was the total GPU memory that was reported wrong, while the other testers reported it was the available GPU memory that was wrong (that was fixed in 7.0.36),
the fix for the Total GPU memory Bug should be in Boinc 7.0.37

Claggy

Is this just a Linux issue or across Windows too, I haven't seen it in Windows but I have in Linux.
____________

Will be the currently BOINC DEV-V7.0.36 maybe the new recommended version in near future?

Probably not, as it still has half the Wacky GPU memory reporting Bug, in my case it was the total GPU memory that was reported wrong, while the other testers reported it was the available GPU memory that was wrong (that was fixed in 7.0.36),
the fix for the Total GPU memory Bug should be in Boinc 7.0.37

Claggy

Is this just a Linux issue or across Windows too, I haven't seen it in Windows but I have in Linux.

As far as i know it was just Windows, as the only testers that responded in the Boinc Alpha list were running Windows (and the private drops were only for Windows), doesn't mean that it doesn't also effect Linux,
you could try Boinc 7.0.36 and see if it is partially fixed. (The available memory should be fixed)